The invention relates generally to hydrophilic polymers with viscoelastic memory and to the use of such polymers, particularly polyethylene oxide (PEO), to produce single-use, auto-destruct (self-annulling) injection devices. Such injection devices, through the polymer of the invention, are rendered inoperative after a single injection without requiring any positive action on the part of the user.
The risk of the transmission of disease through the use of unsterile syringes and needles is of high concern to health care personnel. Childhood immunization requires some five injections, the safety of which must be assured if an immunization program is to achieve and maintain universal acceptance. The inadvertent transmission of disease during immunization is eliminated if one sterile syringe and one sterile needle are used for each injection. Consequently, it has become a priority among health care organizations to develop disposable injection devices that are inexpensive, cannot be used more than once, and can be introduced with little or no vaccinator retraining.
A single-use, self-annulling injection syringe has been disclosed and claimed in U.S. Pat. No. 4,781,683 ('683) which is incorporated herein by reference. The syringe of the '683 patent achieves single-use goals by the action of an insert pressed within the barrel of a conventional syringe with attached needle (cannula). The insert, in one embodiment, is composed of a crosslinked, hydrophilic polymer plug which swells upon contact with the water in the drug/vaccine being injected and thereby blocks the flow channel in the syringe. Therefore, the '683 patent provides for an inexpensive, single-use, and easy-to-use syringe.
Potential problems remain, however. The insert of the '683 patent can take up to 30 minutes to render the syringe inoperative which may be sufficient time to permit substantial reuse of the syringe. Further, if the hydrophilic plug is dehydrated, it might shrink to its original size rendering the syringe operative again. Finally, to enhance manufacturability, a different design for the plug/insert than those disclosed in the '683 patent is desirable.